My '90 740 turbo was getting terrible fuel mileage and getting a 2-3-2 code from the on-board diagnostic box.

Along with cleaning the throttle body and idle control valve, replacing plugs, etc, I replaced the coolant temperature sensor (the one that sends engine temp info to the computer, not the dashboard gauge).

After replacing the sensor, the car was very hard to start, which I attributed to perhaps my knocking something loose. I fiddled around for a while, and then was able to get it to start. I drove it for an hour and it ran very well (though the service engine light came on, which was a new occurance).

The next morning, it was VERY hard to start, and I fooled around checking for spark and fuel, etc., all of which seemed fine.

Finally, it started and drove well, but alas, the service engine light came on again.

I checked the on-board codes, which now read 1-2-3: "No signal from coolant temperature sensor." (!?)

I've never had this code before (and starting has never been a problem).

What gives?

Did I get a bad sensor? I got this one from Auto Zone.

Should I buy another and try again?

Thanks for any advice.